Production of guanidine nitrate



Patented Aug. 12, 1941 PRODUCTION OF GUANIDINE NI'I'CRATE William H. Hill, Mount Lebanon, Pa., and Robert C. Swain, Riverside, and Joseph H. Paden, Glenbrook, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application October 20, 1940, Serial No. 363,306

7 Claims.

This invention relates to a method of preparing guanidine nitrate from cyanamide and/or dicyandiamide as starting materials. Objects of the invention are to provide an eflicient method for the production of guanidine nitrate of high purity by a processv that can be carried out on a large scale without danger from exothermic reactions and with high yields of the desired prodnot.

I In our copending application Serial No. 302,136, filed October 31,1939, we have described a general method of preparing guanidine salts from cyanamide and dicyandiamide by heating these materials. in a solvent comprising liquid ammonia in the presence of an anion capable of combining with guanidine to form a stable guanidine salt. The nitrate ion was stated to be suitable for use in preparing guanidine nitrate by this method. The present application isa continuation-in-part of the above described application, whichhas now issued as Patent No. 2,221,- 4'78, dated November 12, 1940, and deals with the specific application of the general principles of our discovery to the commercial manufacture of guanidine nitrate.

We have discovered thatrguanidine nitrate can be prepared by heating a dispersion of cyanamide r dicyandiamide in the presence of liquid ammonia if the nitrate ion or radical (N03) is presant to combine with the guanidine when it is formed. The nitrate ion or radical may be introduced as free nitric acid or its anhydride N205 (although in the latter case water must also be present) but since both of these methods of introduction will result merely in the formation of ammonium nitrate it is preferable to employ this; salt as a starting material. The nitrate ion may also be; added as a salt of any othertbase wealrerthan the guanidine to be formed 01min any other formin which it iscapable of combining with guanidine to form a stableguanidine a )It is known that melamine is formed when oranamide or dicyandiamide is heated at reaction temperatures in the presence of'liquid ammonia.

which guani din'e combineswithmore cithe starting material to form melamine with regeneration of the ammonia by the reactions We believe that when cyanamide or dicyandiamide is heated with anhydrous ammonia in the presence of the nitrate radical the radical binds the guanidine as a stable guanidine salt in such a manner that it is no longer free to combine with further amounts of cyanamide or dicyandiamide to form melamine or other cyanamide that ammonia is an essential constituent in the Under these conditions we believe that a part of.

process of our invention. Liquid ammonia is a solvent both for cyanamide and dicyandiamide and for ammonium nitrate, and ordinarily a solution of these ingredients in liquid ammonia will be charged into an autoclave. Upon heating, however, the ammonia evaporates as its critical temperature is about 132 C., and it is probable that the greater part of the conversion takes place in the autoclave while at least some of the ammonia is in the vapor phase. It should be understood, therefore, that in claiming the step of heating a solution of the reagent in a solvent comprising essentially. liquid ammonia we of course intend to include this heating step when ammonia is present as a gas by reason of the high reaction temperatures.

A wide variation in the ratio of ammonia to the other constituents of the reaction mixture may-be employed in practicing our invention.

In general, we find that a mixture containing 20-75% of a mixture of ammonium nitrate and cyanamide or dicyandiamide and 25-80% of liquid ammonia can be employed, but we prefer to use a solution containing 50-70% of the ammonium nitrate-cyanamide or dicyandiamide mixture and 30-50% of liquid ammonia. With considerably less than 25% of ammonia there is difficulty in maintaining the reagents in solutionin the autoclave, and in some cases there is evidence of an exothermic reaction, while too high a content of liquid ammonia results, in a lowerand in reduced yields of guanidine nitrate.

The amount of nitrate radical used in the form of ammonium nitrate or its equivalent in making up the autoclave charge is preferably the molecular equivalent of the amount of guanidine to be produced from the cyanamide or dicyandiamide or slightly less. In other words, we prefer to use about 2 moles of ammonium nitrate for each mole of dicyandiamide or one mole of ammonium nitrate for each mole of cyanamide in charging the autoclave. Considerable deviation from these ratios can be resorted to within the scope of our invention, as is illustrated in the following examples. but quantities approximatingthe theoretical ratio are preferable.

As has been noted above, there is no good reason for employing a nitrate other than ammonium nitrate as an ingredient in charging the autoclave, inasmuch as this salt is both relatively cheap and easily soluble in liquid ammonia. It should be understood, however, that-our invention in its broader aspects is not limited to the addition of ammonium nitrate as such to the charge, as the same result can be obtained by adding equivalent amounts of nitric acid to the liquid ammonia; Small amounts of water may also be present, as an impurity in the ammonium nitrate or for other reasons, and it should be understood that the term liquid ammonia is not intended to exclude the presence of small amounts of water. Organic diluents may also be present in the liquid ammonia such as methyl alcohol, ethyl alcohol, or hydrocarbons such as toluol, but usually such diluents are not needed since cyanamide, dicyandiamide, and ammonium nitrate are all freely soluble in liquid ammonia itself. The chief advantage obtainable by the use of such diluents would be to reduce the autoclave pressure at unusually high operating temperatures where the autogenic pressure of.

the reaction may be quite high.

In applying the principles of our invention for the production of guanidine nitrate a pressure vessel should be used, for the range of reaction temperatures may be as much as 200 C. or even considerably higher. Although some reaction can be noted at temperatures as low as 80-100 C. .the lowest practical operatingrtemperature for guanidine nitrate manufacture is about 120 C. and a temperature range of 140- 180'C. appears to be the optimum. In general, the speed of cyanamide or dicyandiamide conversion to guanidine nitrate doubles with each C. rise in temperature, in accordance with the classical rule, and the upper temperature limit is the decomposition temperature of the guanidine nitrate product. As a practical matter, however, temperatures about 250-270 C. would hardly ever be employed, as there maybe an explosionhazard at these temperatures. On

the other hand it appears to be quite feasible to the addition of non-aqueous diluents, and the.

mixture is charged intov an autoclave provided with a stirrer tokeep the liquid in circulation during the heatingperiod. Aiterheating the ,7

autoclave may be cooled and the charge collected and heated to drive off the ammonia. Another method which we have used with success consists in discharging the contents of the autoclave directly into a body of water, from which crystals of almost chemically pure guanidine nitrate can be obtained directly by cooling and crystallization. In this case the ammonia is recovered by separating the mother liquor from the crystals and stripping it with steam in an ordinary ammonia stripping column, from which the ammonia gas may be condensed in the usual manner and reused as a solvent for making up further autoclave charges.

The invention will be illustrated in greater detail by the following specific examples. It should be understood, however, that although these examples may describe certain of the more specific features of the invention they are given primarily for purposes of illustration and in its broader aspects the invention is not limited thereto.

Example 1 10.8 parts by weight of recrystallized dicyandiamide and 20.4 parts of ammonium nitrate were dissolved in 19.2 parts of liquid ammonia and the mixture was charged into an autoclave composed of stabilized l8-8 chrome nickel steel provided with internal heating coils and an agitator. The autoclave was heated by pumping a mixture of diphenyl and diphenyl oxide heat transfer liquid, known commercially as Dowtherm, at l60-180 C. through the coils. The charge was heated to C. and maintained at this temperature for /2 hour. The autoclave was then cooled and discharged and the ammonia was evaporated from the resulting product.

27.5 parts by weight of a product analyzing 90.4% guanidine nitrate were recovered, this amounting to a yield of 79.8%. The solid product was found to contain 5.4% of ammonium nitrate and 0.56% of unreacted dicyandiamide.

Example 2 Example 3 The process oi Example '2 was repeated,'but the temperature of the charge in the autoclave was maintainedat 160 C. for 1 hour, after which it was cooled. 29.9 parts by weight of a solid product were obtained which analyzed 92.9% guanidine nitrate, 3.2% ammonium nitrate and 0.27% dicyandiamide. This constituted a 89.1% yieldof guanidine, nitrate. H

Example 4 The process of Example 3 was repeated, using the same quantities of materials, but the autoclave charge was heated to C. and main tained at this temperature for /2 hour. During this time a pressure of 1650 pounds per sq. in. was developed.

'Upon cooling and discharging the autoclave and evaporating the ammonia, 30.5 parts by Example The'process of Example 4 was repeated, but the autoclave charge was maintained at 170 C.

charge was heated to 170 C. and maintained at this temperature for hour, after which the autoclave was cooled and discharged. The total solids recovered amounted to 39.0 parts, of which 91.0% was guanidine nitrate and 5.3% was ammonium nitrate. No unconverted dicyandiamide was found in the product.

Example for 11/2 hours and then cooled A maximum m 13.5 parts by weight of dicyandiamide, 25.0 pressure of 1800 pounds per sq. in. was developed P f of ammomum pifwts of in the autoclave during this time liquid ammonia were stirred together until soluparts by Weight of a solid product analyb tion occurred and the charge was heated in the ing 93.4% guanidine nitrate, 3.4 parts ammonium auwclave of Example 1 for 1 hour 1 The nitrate and no dicyandiamide were obtained, 50nd product analy zed guan dine nitrate, this amounting to an overall yield of guanidine 39% ammomum mtmte and dmyandlamlqe nitrate of 93% and. amounted to 37.0 parts by weight, or a guani- Example 6 dine nitrate yield of 90.3% of theory. 10.9 parts by weight of dicyandiamide, 20.4 Example 11 parts of ammonium nitrate and 19.2 parts of The process of Example 10 was repeated, using liquid ammonia were agitated (together in a the same reaction times and temperatures but closed chamber until a clear solution was ob- 1.28 parts by weight of water (5% based on the tained. This solution was then pumped into ammonium nitrate) was added to the autoclave the autoclave described in Example 1, heated 95 charge. The solid product obtained after evapto. 180 C. and maintained at this temperature orating off the ammonia and water amounted to for 0.5 hour with a maximum autoclave pres- 37.4 parts and analyzed 91.3% guanidine nitrate, sure of 1950 pounds per sq. in. A 96% recovery 4.9% ammonium nitrate, and 0.68% urea. This of the solids was obtained after evaporating indicates that the presence of small amounts off the ammonia, this constituting 29.9 parts by of water as impurity in the ammonium nitrate weight of a solid product analyzing 89.9% guaniis not particularly objectionable unless a product dine nitrate, 4.9% ammonium nitrate and no free from ureais desired. unreacted dicyandiamide. Example 12 Example 7 12.5 parts by weight of dicyandiamide and 25 10.8 parts ofv dicyandiamide and 21.0 parts of parts of mm nitrat? were dissolved in 24 ammonium nitrate were dissolved in 12.8 parts parts of hqmdammonia m the usual manner of liquid ammonia and heated at 190 c. for 1 and heated for V2 hour at the ailmhour in the autoclave described in Example 1. Y The Solid obtained after 31.0 parts of a solid product were obtained, after 40 mung Off the was found to comfam evaporating off the ammonia, which analyzed of guamdme mtmte 1 of ammomum 873% guanidine nitrate, 73% ammonium nitrate and no unconverted. dicyandiamide. The trate and no unconverted dicyandiamide. This guanidine nitrate yield amounted to 91-1% of amounted to a guanidine nitrate yield of 87.5% theoryof the theoretical. Example 13 Example 8 In order to demonstrate the influence of vary- 2 ing ratios of total solids to ammonia in the 15.25 parts of dicyandiamide, 29.7 parts of autoclave charge, a number of runs were made ammonium nitrate and 27.1 parts of liquidamfollowing the procedure outlined in Example 1. monia were agitated together in a closed vessel The results obtained are given in the following until solution occurred. The charge was then table, in which the parts are by weight, and in pumped into the autoclave described in Example which GN means guanidine nitrate and Dicy. 1, heated to 160 C. and maintained at this temmeans dicyandiamide.

- Molar Time Temp e g t Weight :921; L? 5:15 Dlcy- NHiNO ratio hours 0. GNin solid GN in gent 23g?- soln. solid yield (,MMM

perature for 1 hour after which it was cooled In the foregoing runs the contents of the autoand the ammon a evaporated 43.7 P s of clave, including the ammonia, were discharged a product were obtained analyzing 91.2% guanidirectly into warm water and in all cases clear dine nitrate, 5.3% ammonium nit ate a d n0 solutions were obtained. On cooling, guanidine dicyandiamide A guanidine n trate yield nitrate crystallized out and the quantities and agiijountng t0 Of t y Was thereby purity of the crystals are given in the tables as o aine Example 9 Weight solid and Percent GN in solid respectively. The filtrates from the crystallization were.

made up to 2500 parts for analysis and the guanidine nitrate remaining in solution is given in the column headed Percent GN in soln. The unchangeddicyandiamide was determined by analysis of the filtrates.

' Example 14 vented in the usual manner and the ammonia evaporated from the charge.

The crude product after drying contained 92.4% of guanidine nitrate and a substantially pure product was obtainable by a single recrystallization from an alcohol-benzcl mixture.

What we claim is:

' 1. A method for the manufacture of guanidine nitrate which comprises heating, at a temperature between about 120 C. and the decomposition temperature of guanidine nitrate and under the corresponding autogenic pressure, a solution of a member of the group consisting of cyanamide and dicyandiamide in a solvent comprising essentially liquid ammonia in the presence of a nitrate ion capable of combining with guanidine to form a stable guanidine salt.

2. A method of producing guanidine nitrate which comprises heating, at temperatures between about 120 C. and the decomposition temperature of guanidine nitrate and under the corresponding autogenic pressure, a solution of a member of the group consisting of cyanamide and dicyandiamide in a solvent comprising essentially liquid ammonia in the presence of ammonium nitrate.

3. A method of producing guanidine nitrate which comprises heating, at temperatures between 80 C. and the decomposition temperature of the guanidine salt and under the corresponding autogenic pressure, a dispersion of dicyandiamide and ammonium nitrate in a solvent comprising essentially liquid ammonia.

4. A method for the manufacture of guanidine nitrate which comprises heating in a closed vessel at a temperature between about 120 C. and the decomposition temperature of guanidine nitrate a solution containing -75% of a mixture of ammonium nitrate and a member of the group consisting of cyanamide and dicyandiamide and -80% of liquid ammonia.

5. A method for the manufacture of guanidine nitrate which comprises heating in a closed vessel at a temperature between about 120 C. and the decomposition temperature of guanidine nitrate a solution containing -70% of a mixture of ammonium nitrate and a member of the group consisting of cyanamide and dicyandiamide and 30-50% of liquid ammonia.

6. A method of producing guanidine nitrate which comprises the steps of heating a mixture of ammonium nitrate and a member of the group consisting of cyanamide and dicyandiamide in a solvent comprising essentially liquid ammonia at temperatures between about C. and the decomposition temperature of the prodnot and under the corresponding autogenic pressure until guanidine nitrate is formed, mixing the charge with water, and crystallizing out guanidine nitrate.

'7. A method according to claim 6 in which the mother liquor is separated from the crystals and the ammonia is stripped therefrom and reused in the process.

WILLIAM H. HILL. ROBERT C. SWAIN. JOSEPH H. PADEN. 

